Lead titanate (PbTiO3) having a perovskite structure (general formula ABO3) is ferroelectric and suited as a piezoelectric material because of its exhibition of piezoelectricity. It has a small number of pores and it is difficult to obtain strong ceramic using this lead titanate. Research and development of a method to obtain a dense piezoelectric ceramic composition by substituting an element such as Ca, Sr, Zn or W for a part of Pb or Ti or by adding various types of components to the lead titanate was undertaken, and practicable application of the piezoelectric ceramic composition to a piezoelectric part such as a piezoelectric ceramic oscillator is being made.
If the piezoelectric part is a stacked type, it is efficient to manufacture the piezoelectric part by alternately stacking ceramic layers and conductive layers and collectively firing these conductive and ceramic layers.
Furthermore, expensive refractory noble metals such as Pt or Pd were initially used as an internal electrode material forming each conductive layer. Recently, however, a conductive material obtained by mixing a relatively inexpensive metal such as Ag to such expensive noble metals or an Ag—Pd alloy conductive material has been investigated.
As the internal electrode material, it is preferable to use a metal industrially available at low cost or to use a mixture or an alloy containing many low-cost metals. However, the low-cost metals normally have a low melting point. Due to this, it is necessary to make the firing temperature low if such a low-melting metal is used as the internal electrode material and the conductive layers and the ceramic layers are collectively fired. In other words, if a lead titanate-based ceramic material having a lower firing temperature can be obtained, a low-cost metal or metals can be used as the internal electrode material and the manufacturing cost of the piezoelectric part can be reduced accordingly.
As a technique for low-temperature firing a lead titanate-based piezoelectric material, there is conventional proposed a piezoelectric ceramic composition main components of which are represented by a general formula Pba(COα/2W(2-α/2)bTi1-bO3 with a, b, and α satisfying 0.90≦a≦1.05, 0.01≦b≦0.33, and 1.01≦α≦1.10 (Patent Document 1).
According to Patent Document 1, a piezoelectric ceramic composition that can be fired at a low temperature equal to or lower than 1000° C. and that can provide a sintered compact having less deformation during firing can be obtained by setting a, b and α in the general formula to fall within these predetermined ranges, respectively.
As another technique for low-temperature firing a lead titanate-based ceramic material, there is proposed a composition represented by a general formula [(PbaMeb) {(Ni1/3Nb2/3)xTiy(Zn1/2W1/2)z}O2+a+b] (where x+y+z=1, Me is at least one member selected from among the group consisting of Ca, Sr and Ba), although this composition is a dielectric ceramic composition (Patent Document 2).
According to Patent Document 2, a high-dielectric-constant dielectric ceramic composition that can be fired at a low temperature equal to or lower than 1100° C. can be obtained by setting a, b, x, y and z in the general formula to fall within predetermined ranges, respectively.
Patent Document 1: Japanese Unexamined Patent Publication No. 2003-165770
Patent Document 2: Japanese Examined Patent Publication No. 7-12975